Tunnel provisioning with link aggregation

ABSTRACT

A method for processing data packets in a communication network includes establishing a path for a flow of the data packets through the communication network. At a node along the path having a plurality of aggregated ports, a port is selected from among the plurality to serve as part of the path. A label is chosen responsively to the selected port. The label is attached to the data packets in the flow at a point on the path upstream from the node. Upon receiving the data packets at the node, the data packets are switched through the selected port responsively to the label.

FIELD OF THE INVENTION

The present invention relates generally to communication networks, andparticularly to methods and systems for performing link aggregation intunneled networks.

BACKGROUND OF THE INVENTION Multiprotocol Label Switching

Multiprotocol Label Switching (MPLS) has gained popularity as a methodfor efficient transportation of data packets over connectionlessnetworks, such as Internet Protocol (IP) networks. MPLS is described indetail by Rosen et al., in Request for Comments (RFC) 3031 of theInternet Engineering Task Force (IETF), entitled “Multiprotocol LabelSwitching Architecture” (January, 2001), which is incorporated herein byreference. This RFC, as well as other IETF RFCs cited hereinbelow, isavailable at www.ietf.org/rfc.

In MPLS, each packet is assigned to a Forwarding Equivalence Class (FEC)when it enters the network, depending on its destination address. Thepacket receives a fixed-length label, referred to as an “MPLS label”identifying the FEC to which it belongs. All packets in a given FEC arepassed through the network over the same path by label-switching routers(LSRs). The flow of packets along a label-switched path (LSP) under MPLSis completely specified by the label applied at the ingress node of thepath. Therefore, an LSP can be viewed as a tunnel through the network.

MPLS defines a label distribution protocol (LDP) by which one LSRinforms another of the meaning of labels used to forward traffic betweenand through them. Another example is RSVP-TE, which is described byAwduche et al., in IETF RFC 3209 entitled “RSVP-TE: Extensions to RSVPfor LSP Tunnels” (December, 2001), which is incorporated herein byreference. RSVP-TE extends the well-known Resource Reservaticn Protocol(RSVP), allowing the establishment of explicitly-routed LSPs using RSVPas a signaling protocol. RSVP itself is described by Braden et al., inIETF RFC 2205, entitled “Resource ReSerVation Protocol (RSVP)—Version 1Functional Specification” (September, 1997), which is incorporatedherein by reference.

Section 1 of RFC 2205 defines an “admission control” decision module,which is used during reservation setup to determine whether a node hassufficient available resources to supply the requested quality ofservice. The admission control module is used in RSVP-TE for setting upMPLS tunnels.

U.S. Patent Application Publication US 2002/0110087 A1, entitled“Efficient Setup of Label-Switched Connections,” whose disclosure isincorporated herein by reference, describes methods and systems forcarrying layer 2 services, such as Ethernet frames, throughlabel-switched network tunnels.

Ethernet Link Aggregation

Link aggregation (LAG) is a technique by which a group of parallelphysical links between two endpoints in a data network can be joinedtogether into a single logical link (referred to as a “LAG group”).Traffic transmitted between the endpoints is distributed among thephysical links in a manner that is transparent to the clients that sendand receive the traffic. For Ethernet networks, link aggregation isdefined by Clause 43 of IEEE Standard 802.3ad, Carrier Sense MultipleAccess with Collision Detection (CSMA/CD) Access Method and PhysicalLayer Specifications (2002 Edition), which is incorporated herein byreference. Clause 43 defines a link aggregation protocol sub-layer,which interfaces between the standard Media Access Control (MAC) layerfunctions of the physical links in a link aggregation group and the MACclients that transmit and receive traffic over the aggregated links.

U.S. Patent Application Publication US 2004/0228278 A1, entitled“Bandwidth Allocation for link Aggregation,” whose disclosure isincorporated herein by reference, describes methods for bandwidthallocation in a link aggregation system. The methods described in thispublication are meant to ensure that sufficient bandwidth will beavailable on the links in the group in order to meet service guarantees,notwithstanding load fluctuations and link failures.

SUMMARY OF THE INVENTION

In currently available communication equipment, there is no coordinationbetween the operation of the RSVP-TE admission control module,responsible for allocating bandwidth for newly provisioned MPLS tunnels,and the Ethernet link-aggregation port allocation function. The linkaggregation process is completely transparent to the RSVP-TE tunnelprovisioning process, as the latter views the aggregated group ofEthernet ports as a single, high-capacity logical port. The linkaggregation process (i.e. the distribution of frames among the physicalports), on the other hand, is not aware of the bandwidth allocationperformed by the RSVP-TE admission control module when assigning a portto a given flow of packets. This lack of coordination may cause severalproblems. For example:

-   -   When reserving bandwidth for a new MPLS tunnel, the admission        control module considers only the total available bandwidth of        the entire LAG group of Ethernet ports. The bandwidth        availability of individual ports is not typically visible to the        admission control module. Therefore, the actual total bandwidth        transmitted to a port may be far greater than the actual        available bandwidth of any individual port. The LAG process, on        the other hand, typically directs all packets with the same        header attributes (such as all packets belonging to the same        tunnel) through a single Ethernet port in the LAG group. This        process is known as frame distribution or hashing. This        contradiction may result in poor service quality, since multiple        flows may be directed to the same Ethernet port, which may be        unable to deliver the bandwidth allocated by the RSVP-TE        admission control module.    -   The link aggregation process does not guarantee bandwidth in the        event that one or more Ethernet ports fail or are taken out of        service. It is desirable to guarantee the allocated bandwidth of        an MPLS tunnel during port failure or reconfiguration.

Embodiments of the present invention provide coordination between tunnelprovisioning and the link aggregation process. The disclosed methods andsystems ensure that all packets belonging to a certain tunnel will betransmitted through a single physical port, and that sufficientbandwidth will be allocated for the tunnel on the selected port. Methodsfor bandwidth protection, in order to maintain the allocated bandwidthfor the tunnel during port failure or reconfiguration are also disclosedherein.

Although the embodiments described hereinbelow relate specifically toprovisioning of MPLS tunnels over aggregated Ethernet ports, theprinciples of the present invention may also be applied to othertunneling schemes, such as Generic Routing Encapsulation (GRE), LayerTwo Tunneling Protocol (L2TP) and other link aggregation mechanisms.

There is therefore provided, in accordance with an embodiment of thepresent invention, a method for processing data packets in acommunication network, including:

establishing a path for a flow of the data packets through thecommunication network;

at a node along the path having a plurality of aggregated ports,selecting a port from among the plurality to serve as part of the path;

choosing a label responsively to the selected port;

attaching the label to the data packets in the flow at a point on thepath upstream from the node; and

upon receiving the data packets at the node, switching the data packetsthrough the selected port responsively to the label.

In a disclosed embodiment, the path includes a tunnel through thecommunication network. In another embodiment, the tunnel includes a MPLS(Multi-Protocol Label Switching) tunnel, and establishing the pathincludes receiving and responding to a RSVP-TE (Resource ReservationProtocol) PATH message.

In yet another embodiment, the plurality of aggregated ports includes aLAG (Link Aggregation) group, according to an IEEE 802.3adspecification.

In still another embodiment, establishing the path includes receiving arequest to establish the path from a preceding node in the communicationnetwork, which is located upstream along the path, and attaching thelabel includes sending the label to the preceding node, to be attachedto the packets sent by the preceding node.

In another embodiment, establishing the path includes receiving anindication of a requested service property of the flow, and selectingthe port includes assigning the port to the flow so as to comply withthe requested service property. In a disclosed embodiment, the requestedservice property includes at least one of a guaranteed bandwidth, a peakbandwidth and a class-of-service. Additionally or alternatively,assigning the port includes selecting the port having a maximumavailable bandwidth out of the plurality of aggregated ports. Furtheradditionally or alternatively, assigning the port includes selecting theport having a minimum available bandwidth out of the plurality ofaggregated ports, which is still greater than or equal to the guaranteedbandwidth.

In another embodiment, switching the data packets includes mapping thedata packets to the selected port responsively to the label.Additionally or alternatively, mapping the data packets includesapplying a hashing function to the label so as to determine a number ofthe selected port, and choosing the label includes applying an inverseof the hashing function to the number of the selected port.

In yet another embodiment, choosing the label includes inserting intothe label one or more bits that correspond to a number of the selectedport, and mapping the data packets includes extracting the one or morebits from the label so as to determine the number of the selected port.

In still another embodiment, choosing the label includes storing thelabel and a number of the selected port in a memory, and mapping thedata packets includes extracting the number from the memory responsivelyto the label so as to determine the number of the selected port.

In another disclosed embodiment, the method includes allocating a portfrom among the plurality of aggregated ports, different from theselected port, to serve as a backup port and, responsively to a serviceinterruption of the selected port, replacing the selected port with thebackup port as part of the path.

There is also provided, in accordance with an embodiment of the presentinvention, apparatus for processing data packets at a node in acommunication network, the apparatus including:

a plurality of aggregated ports, which are arranged to transmit the datapackets over a respective plurality of physical links;

a mapper, which is arranged to receive the data packets from thenetwork, and to map the data packets to the plurality of aggregatedports for onward transmission; and

a processor, which is arranged to establish the path for a flow of thedata packets through the communication network, to select a port fromamong the plurality of aggregated ports to serve as part of the path, tochoose a label responsively to the selected port, and to cause thechosen label to be attached to the data packets in the flow at a pointon the path upstream from the node, so that the mapper, upon receivingthe data packets, switches the data packets through the selected portresponsively to the label.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram that schematically illustrates an MPLScommunication network, in accordance with an embodiment of the presentinvention;

FIG. 1B is a block diagram that schematically illustrates an MPLS/LAGswitch, in accordance with an embodiment of the present invention;

FIG. 2 is a block diagram that schematically illustrates an encapsulatedMPLS packet, in accordance with an embodiment of the present invention;

FIG. 3 is a flow chart that schematically illustrates a method for portallocation, in accordance with an embodiment of the present invention;and

FIG. 4 is a flow chart that schematically illustrates a method for portallocation, in accordance with another embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1A is a block diagram that schematically illustrates a computercommunication network 20, in accordance with an embodiment of thepresent invention. System 20 comprises two MPLS networks 22, labeled Aand B, i.e., networks containing MPLS-capable switches. (Typically,these networks may also carry non-MPLS traffic, as in MPLS-capable IPnetworks that are known in the art.) MPLS networks A and B are connectedvia MPLS/LAG switches 26, using N physical Ethernet ports 24. Ports 24are aggregated into a LAG group 25 using link aggregation (LAG) methodsdefined in the IEEE 802.3ad specification cited above. The two MPLS/LAGswitches 26, which also function as LSRs, perform link aggregation andother packet routing/switching functions, according to methods whichwill be described below.

An MPLS tunnel 28 (a label switched path, or LSP, according to the MPLSspecification cited above) is established from an ingress node in MPLSnetwork A, through the two switches and the LAG group, to an egress nodein MPLS network B. (The ingress and egress nodes are not shown in thefigure.) The tunnel forms a path over which data frames traverse fromthe ingress node to the egress node. In the exemplary configuration ofFIG. 1A, the MPLS tunnel is switched through one of ports 24, labeled“PORT 3.” The term “downstream” typically denotes the direction ofpacket flow from the ingress node to the egress node along the tunnel.The term “upstream” denotes the opposite direction. The term “hop”denotes a part of the tunnel that connects two consecutive LSRs.

As part of the MPLS tunnel provisioning process (which is described inRFC 3031) each LSR along tunnel 28 attaches an MPLS label to the packetsit transmits downstream to the next LSR, identifying the packets thatbelongs to tunnel 28. Thus, in the example shown in FIG. 1A, MPLS/LAGswitch A receives packets to which MPLS labels have been attached at apreceding node 29, which is an LSR located in MPLS network A, upstreamfrom MPLS/LAG switch A. In most MPLS implementations, a given MPLS labelis used within a single hop along the tunnel. In this case node 29 isthe LSR that immediately precedes MPLS/LAG switch A in tunnel 28. Inother MPLS implementations, the same label may be used for severaladjacent hops of the tunnel, so that there may be one or more additionalLSRs located between node 29 and switch A.

The exemplary network configuration shown in FIG. 1A was chosen for thesake of conceptual clarity. Other tunneled network configurations withlink aggregation may use the methods and systems disclosed herein, aswill be apparent to those skilled in the art. As noted earlier, theseconfigurations may use MPLS and Ethernet LAG or other tunneling and linkaggregation protocols known in the art.

FIG. 1B is a block diagram that schematically shows details of MPLS/LAGswitch 26, in accordance with an embodiment of the present invention. Onthe transmitting side of the LAG group, the switch typically receives anMPLS payload, encapsulated in Ethernet frames from the ingress node(either directly or via other LSRs in MPLS network A). Switch 26switches the MPLS payload according to the MPLS label andre-encapsulates the MPLS payload into an Ethernet frame destined to theLAG group. Following the MPLS switching process, the MPLS switchperforms the LAG function and maps the Ethernet frame to one of thephysical Ethernet ports 24 of LAG group 25. On the receiving side of theLAG group, the switch collects the Ethernet frames from the ports of LAGgroup 25 and sends them to the egress node (either directly or via otherLSRs, as defined by the tunnel).

Switch 26 comprises an RSVP-TE processor 30 and a CAC (ConnectionAdmission Control) processor 32, which handle MPLS tunnel provisioningand the associated signaling. Although processors 30 and 32 are shown,for the sake of conceptual clarity, as separate functional units, inpractice these two functions are typically implemented as softwareprocesses on the same processor. Practically speaking, they maygenerally be regarded as a single processor, regardless ofimplementation. Switch 26 also comprises a mapper 34, which maps eachMPLS payload to a specific physical Ethernet port 24 (following thepayload encapsulation into an Ethernet frame), according to methodswhich will be described below.

The methods described herein typically address a unidirectional packetflow, i.e., packets flowing from MPLS network A to MPLS network B. Themethods are presented in this way because MPLS tunnels areunidirectional by definition. This fact does not limit the disclosedmethods in any way to unidirectional message flows. Bidirectional packetflow is typically implemented by setting up two separate, independentMPLS tunnels.

MPLS/LAG switch 26 may be implemented using a network processor, whichis programmed in software to carry out the functions described hereinand is coupled to suitable hardware for interfacing with the MPLSnetwork and Ethernet ports. Switch 26 may either comprise a standaloneunit or may alternatively be integrated with other computing functionsof the network processor. Some or all of the functions of switch 26 canalso be implemented using a suitable general-purpose computer, aprogrammable logic device, an application-specific integrated circuit(ASIC) or a combination of such elements.

FIG. 2 is a block diagram that schematically illustrates an MPLS packetencapsulated into an Ethernet II format, in accordance with anembodiment of the present invention. The Ethernet frame comprises a MAC(Media Access Control) destination address field 40, a MAC sourceaddress field 42, and an Ethertype identifier field 46 used to identifythe specific protocol. The frame ends with a frame check sequence (FCS)field 48 used for error detection. The encapsulated MPLS packetcomprises an MPLS header 50, which comprises an MPLS label field 52. AnMPLS payload field 54 comprises the message body, containing informationtransmitted by the MPLS packet. In some implementations, the frame alsocomprises optional VLAN Ethertype and VLAN tag fields.

Mapper 34 of switch 26 performs a mapping function that uses informationcarried in one or more fields of the encapsulated MPLS packet to selectthe physical Ethernet port for mapping the packet. The IEEE 802.3adstandard cited above does not dictate any particular mapping method forlink aggregation, other than forbidding frame duplication and requiringthat frame ordering be maintained over all frames in a given flow. Inpractice, to meet these requirements, the mapper typically maps allframes in a given MPLS tunnel to the same physical port.

The mapping function typically uses MPLS label 52 for mapping, since theMPLS label uniquely identifies MPLS tunnel 28, and it is required thatall MPLS packets belonging to the same tunnel be switched through thesame physical port 24. Additionally or alternatively, the mappingfunction uses a “PW” label (pseudo wire label, formerly known as avirtual connection, or VC label), which is optionally added to MPLSheader 50. The PW label comprises information that the egress noderequires for delivering the packet to its destination, and is optionallyadded during the encapsulation of MPLS packets. Additional detailsregarding the VC label can be found in an IETF draft by Martini et al.entitled “Encapsulation Methods for Transport of Ethernet Frames OverIP/MPLS Networks” (IETF draft-ietf-pwe3-ethernet-encap-07.txt, May,2004), which is incorporated herein by reference. In some embodiments,mapper 34 applies a hashing function to the MPLS and/or PW label, aswill be described below.

Port Coding

FIG. 3 is a flow chart that schematically illustrates a method for portallocation using port coding, in accordance with an embodiment of thepresent invention. This method, as well as the method of FIG. 4described below, is used to provision MPLS tunnel 28 by allocatingbandwidth on one of the physical ports of LAG group 25.

The method of FIG. 3 begins when the preceding node asks to establish apart of tunnel 28 (comprising one or more hops) for sending MPLS packetsto MPLS/LAG switch 26 A. The preceding node requests and then receivesthe MPLS label, which it will subsequently attach to all packets thatare sent to MPLS/LAG switch 26 labeled A. The preceding node sendsdownstream an RSVP-TE PATH message augmented with a LABEL_REQUESTobject, as defined by RSVP-TE, to MPLS/LAG switch A, at a labelrequesting step 60. The PATH message typically comprises informationregarding service properties that are requested for tunnel 28. Theservice properties may comprise a guaranteed bandwidth (sometimesdenoted CIR—Committed Information Rate) and a peak bandwidth (sometimesdenoted PIR—Peak Information Rate), as well as a requested CoS (Class ofService—a measure of packet priority).

CAC processor 32 of switch A receives the PATH message and extracts therequested service properties. The CAC processor examines the availablebandwidth of all ports 24 in LAG group 25 and selects a single physicalport (“the selected physical port”) on which to allocate bandwidth forMPLS tunnel 28, responsively to the requested service properties, at aport selection step 62. The selected physical port should be capable ofproviding sufficient peak and average bandwidths, as requested by thepreceding node (and, originally, by the ingress node).

In one embodiment the CAC processor selects the physical port having amaximum available bandwidth out of the ports of LAG group 25. Thisapproach attempts to distribute the packet flows evenly among thephysical ports. In an alternative embodiment, the CAC processor mayfollow a “first-to-fill” strategy, i.e., select a physical port thatwill reach the highest utilization after allocating the requestedbandwidth to tunnel 28. Any other suitable selection criteria may beapplied by CAC processor 32. In the event that none of physical ports 24has sufficient available bandwidth to comply with the requested serviceproperties, the CAC processor returns an error message to the precedingnode and denies the provisioning of tunnel 28. After successfullyselecting the physical port, the CAC processor allocates and reservesthe requested bandwidth for tunnel 28.

Regardless of the selection criterion used, the results of step 62 arethat (1) a single physical port is explicitly selected and assigned toMPLS tunnel 28, and (2) sufficient bandwidth is allocated to tunnel 28,considering only the available bandwidth of the selected physical port,rather than the total available bandwidth of LAG group 25. All packetsbelonging to tunnel 28 will be switched through the same selectedphysical port, using the port coding technique described hereinbelow.

Having selected a physical port, RSVP-TE processor 30 of switch A nowgenerates a suitable MPLS label, at a label generation step 64. Thepreceding node upstream of switch A will subsequently attach this MPLSlabel to all MPLS packets transmitted through tunnel 28 to switch A. Thelabel is assigned, in conjunction with the mapping function of mapper34, so as to ensure that all MPLS packets carrying this label areswitched through the physical port that was selected for this tunnel atstep 62. For this purpose, RSVP-TE processor 30 of switch A dedicates asub-set of the bits of MPLS label 52 to encode the serial number of theselected physical port. For example, the four least-significant bits ofMPLS label 52 may be used for encoding the selected port number. Thisconfiguration is suitable for representing LAG groups having up to 16physical ports (N<16). The remaining bits of MPLS label 52 may be chosenat random or using any suitable method known in the art.

RSVP-TE processor of switch 26 sends the generated MPLS label upstreamto the preceding node, using an RSVP-TE RESV message augmented with aLABEL object, at a label sending step 66. At this stage, the part oftunnel 28 between the preceding node and switch A is provisioned andready for use. The preceding node attaches the aforementioned MPLS labelto all subsequent MPLS packets that it sends downstream through tunnel28 to MPLS/LAG switch A, at a packet sending step 68.

Mapper 34 of switch A maps the received packets belonging to tunnel 28to the selected physical Ethernet port at a mapping step 70. For thispurpose, mapper 34 extracts the MPLS label from each received packet anddecodes the selected physical port number from the dedicated sub-set ofbits, such as the four LSB, as described in step 64 above. The decodedvalue is used for mapping the packet to the selected physical port,which was allocated by the CAC processor at step 62 above. In thefour-bit example described above, the mapping function may be writtenexplicitly as: Selected port number=((MPLS label) and (0x0000F)),wherein “and” denotes the “bitwise and” operator.

In an alternative embodiment, RSVP-TE processor 30 generates anarbitrary MPLS label at step 64 and stores this label together with thecorresponding serial number of the selected physical port in a lookuptable or other data structure. At step 70, the mapper extracts the MPLSlabel from each received MPLS packet and queries the lookup table withthe MPLS label value to determine the physical port through which toswitch the packet.

Inverse Hashing

FIG. 4 is a flow chart that schematically illustrates an alternativemethod for port allocation, in accordance with another embodiment of thepresent invention. Similarly to the method shown in FIG. 3 above, themethod begins with the preceding node in MPLS network A asking toestablish a part of MPLS tunnel 28 for sending MPLS packets to switch A.The preceding node sends downstream an RSVP-TE PATH message, at a labelrequesting step 80, which is identical to label requesting step 60 ofFIG. 3 above. CAC processor 32 of switch A receives the PATH message,extracts the requested service properties, and selects a physical portout of group 25, at a port selection step 82. Step 82 is identical toport selection step 62 of FIG. 3 above.

In this method, the mapping function used by mapper 34 of switch A is ahashing function. Various hashing functions are known in the art, andany suitable hashing function may be used in mapper 34. Since thehashing operation is performed for each packet, it is desirable to havea hashing function that is computationally simple.

As mentioned above, the hashing function typically hashes the value ofMPLS label 52 to determine the selected physical port, as the MPLS labeluniquely identifies tunnel 28. For example, the following hashingfunction may be used by mapper 34: Selected port number=1+((MPLS label)mod N), wherein N denotes the number of physical Ethernet ports in LAGgroup 25, and “mod” denotes the modulus operator. Assuming the values ofMPLS labels are distributed uniformly over a certain range, thisfunction achieves a uniform distribution of port allocations for thedifferent MPLS labels. It can also be seen that all packets carrying thesame MPLS label (in other words—belonging to the same MPLS tunnel) willbe mapped to the same physical port.

Returning to the description of FIG. 4, RSVP-TE processor 30 of switch Atakes the serial number of the selected physical port (selected at step82) and generates MPLS label 52 by calculating an inverse of the hashingfunction, at an inverse calculation step 84. The purpose of this step isto choose an MPLS label in a way that would cause the hashing functionof mapper 34 to output the selected physical port (so that allsubsequent packets carrying this label will be switched through thisport). The following numerical example, which uses the hashing functiongiven above, demonstrates the inverse hashing process:

-   -   The inverse of the hashing function given above is: MPLS        label=(Selected port number−1)+N*MPLS_(p), wherein N denotes the        number of physical ports in group 25, and MPLS_(p) denotes a        predetermined number, which is assigned by RSVP-TE processor 30        for each MPLS tunnel. Note that the value of MPLS_(p) does not        affect the hashing function, since different values of MPLS_(p)        only add integer multiples of N to the value of the MPLS label.        The modulus operator of the hashing function eliminates this        effect. This mechanism enables the same hashing/inverse-hashing        functions to generate multiple MPLS labels to support multiple        tunnels.    -   Assume that MPLS_(p)=21882. Assume also that the LAG group has 3        ports (N=3) and that the CAC processor has selected physical        port number 2 at step 82. The MPLS label calculated by the        RSVP-TE processor at step 84 is thus given by: MPLS        label=(2−1)+3*21882=65647

Having generated the MPLS label, RSVP-TE processor of switch A sends theMPLS label upstream to the preceding node, at a label sending step 86,which is identical to label sending step 66 of FIG. 3 above. At thisstage, the part of tunnel 28 between the preceding node and switch A isprovisioned and ready for use. The preceding node attaches theaforementioned MPLS label to all subsequent MPLS packets, belonging totunnel 28, that are sent downstream to MPLS/LAG switch A, at a packetsending step 88.

Mapper 34 of switch A maps each received packet to the selected physicalport of LAG group 25 using the hashing function, at a hashing step 90.Mapper 34 extracts the MPLS label from each received packet and uses thehashing function to calculate the serial number of the selected physicalport, which was selected by the CAC processor at step 82. Following thenumerical example given above, the mapper extracts MPLS label=65647 fromthe packet. Substituting this value and N=3 into the hashing functiongives: Selected port number=1+(65647 mod 3)=2, which is indeed the portnumber selected in the example above.

Lag Protection

The IEEE 802.3ad standard cited above describes a protection mechanismfor cases in which one of ports 24 fails or is intentionally taken outof service for any reason. In this case, the mapping function shoulddistribute the data packets among the remaining ports. When using linkaggregation in conjunction with tunneling methods such as MPLS, allpackets belonging to a given tunnel should be switched through a singleport 24. This property should be maintained in case of failure or portreconfiguration.

In an embodiment of the present invention, one of the N ports 24 of LAGgroup 25 is not used under normal network conditions and is maintainedas a backup port. In the event that one of the active N−1 ports 24 failsor is taken out of service, switch A replaces the failed port with thebackup port. As all ports 24 typically have equal bandwidths, theservice properties required by tunnel 28 can be maintained.

In one embodiment, switch A may revert to the original port as soon asit recovers or returned into service. In an alternative embodiment, oncethe backup port has replaced a failed port, it continues to function asan ordinary port. The failed port, once recovered, begins to function asa backup port.

Although the methods and systems described hereinabove address mainlyMPLS and Ethernet link aggregation, the principles of the presentinvention may also be used in conjunction with other communicationprotocols. For example, the methods described above may be adapted foruse with other types of labeled traffic flows, such as flows labeled inaccordance with other tunneling methods, and other link aggregationmethods.

It will thus be appreciated that the embodiments described above arecited by way of example, and that the present invention is not limitedto what has been particularly shown and described hereinabove. Rather,the scope of the present invention includes both combinations andsub-combinations of the various features described hereinabove, as wellas variations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description and which arenot disclosed in the prior art.

1. A method for processing data packets in a communication network,comprising: establishing a path for a flow of the data packets throughthe communication network; at a node along the path having a pluralityof aggregated ports, selecting a port from among the plurality to serveas part of the path; choosing a label responsively to the selected port;attaching the label to the data packets in the flow at a point on thepath upstream from the node; and upon receiving the data packets at thenode, switching the data packets through the selected port responsivelyto the label.
 2. The method according to claim 1, wherein the pathcomprises a tunnel through the communication network.
 3. The methodaccording to claim 2, wherein the tunnel comprises a MPLS(Multi-Protocol Label Switching) tunnel, and wherein establishing thepath comprises receiving and responding to a RSVP-TE (ResourceReservation Protocol) PATH message.
 4. The method according to claim 1,wherein the plurality of aggregated ports comprises a LAG (LinkAggregation) group, according to an IEEE 802.3ad specification.
 5. Themethod according to claim 1, wherein establishing the path comprisesreceiving a request to establish the path from a preceding node in thecommunication network, which is located upstream along the path, andwherein attaching the label comprises sending the label to the precedingnode, to be attached to the packets sent by the preceding node.
 6. Themethod according to claim 1, wherein establishing the path comprisesreceiving an indication of a requested service property of the flow, andwherein selecting the port comprises assigning the port to the flow soas to comply with the requested service property.
 7. The methodaccording to claim 6, wherein the requested service property comprisesat least one of a guaranteed bandwidth, a peak bandwidth and aclass-of-service.
 8. The method according to claim 7, wherein assigningthe port comprises selecting the port having a maximum availablebandwidth out of the plurality of aggregated ports.
 9. The methodaccording to claim 7, wherein assigning the port comprises selecting theport having a minimum available bandwidth out of the plurality ofaggregated ports, which is still greater than or equal to the guaranteedbandwidth.
 10. The method according to claim 1, wherein switching thedata packets comprises mapping the data packets to the selected portresponsively to the label.
 11. The method according to claim 10, whereinmapping the data packets comprises applying a hashing function to thelabel so as to determine a number of the selected port, and whereinchoosing the label comprises applying an inverse of the hashing functionto the number of the selected port.
 12. The method according to claim10, wherein choosing the label comprises inserting into the label one ormore bits that correspond to a number of the selected port, and whereinmapping the data packets comprises extracting the one or more bits fromthe label so as to determine the number of the selected port.
 13. Themethod according to claim 10, wherein choosing the label comprisesstoring the label and a number of the selected port in a memory, andwherein mapping the data packets comprises extracting the number fromthe memory responsively to the label so as to determine the number ofthe selected port.
 14. The method according to claim 1, and comprising:allocating another port from among the plurality of aggregated ports,different from the selected port, to serve as a backup port; andresponsively to a service interruption of the selected port, replacingthe selected port with the backup port as part of the path. 15.Apparatus for processing data packets at a node in a communicationnetwork, the apparatus comprising: a plurality of aggregated ports,which are arranged to transmit the data packets over a respectiveplurality of physical links; a mapper, which is arranged to receive thedata packets from the network, and to map the data packets to theplurality of aggregated ports for onward transmission; and a processor,which is arranged to establish the path for a flow of the data packetsthrough the communication network, to select a port from among theplurality of aggregated ports to serve as part of the path, to choose alabel responsively to the selected port, and to cause the chosen labelto be attached to the data packets in the flow at a point on the pathupstream from the node, so that the mapper, upon receiving the datapackets, switches the data packets through the selected portresponsively to the label.
 16. The apparatus according to claim 15,wherein the path comprises a tunnel through the communication network.17. The apparatus according to claim 16, wherein the tunnel comprises aMPLS (Multi-Protocol Label Switching) tunnel, and wherein the processoris arranged to receive and respond to a RSVP-TE (Resource ReservationProtocol) PATH message so as to establish the tunnel.
 18. The apparatusaccording to claim 15, wherein the plurality of aggregated portscomprises a LAG (Link Aggregation) group, according to an IEEE 802.3adspecification.
 19. The apparatus according to claim 15, wherein theprocessor is arranged to receive a request to establish the path from apreceding node in the communication network, which is located upstreamalong the path, and to send the label to the preceding node, to beattached to the packets sent by the preceding node.
 20. The apparatusaccording to claim 15, wherein the processor is arranged to receive anindication of a requested service property of the flow, and to assignthe port to the flow so as to comply with the requested serviceproperty.
 21. The apparatus according to claim 20, wherein the requestedservice property comprises at least one of a guaranteed bandwidth, apeak bandwidth and a class-of-service.
 22. The apparatus according toclaim 21, wherein the processor is arranged to select the port having amaximum available bandwidth out of the plurality of aggregated ports.23. The apparatus according to claim 21, wherein the processor isarranged to select the port having a minimum available bandwidth out ofthe plurality of aggregated ports, which is still greater than or equalto the guaranteed bandwidth.
 24. The apparatus according to claim 15,wherein the mapper is arranged to map the data packets to the selectedport responsively to the label.
 25. The apparatus according to claim 24,wherein the mapper is arranged to apply a hashing function to the labelso as to determine a number of the selected port, and wherein theprocessor is arranged to apply an inverse of the hashing function to thenumber of the selected port.
 26. The apparatus according to claim 24,wherein the processor is arranged to insert into the label one or morebits that correspond to a number of the selected port, and wherein themapper is arranged to extract the one or more bits from the label so asto determine the number of the selected port.
 27. The apparatusaccording to claim 24, wherein the processor is arranged to store thelabel and a number of the selected port in a memory, and wherein themapper is arranged to extract the number from the memory responsively tothe label, so as to determine the number of the selected port.
 28. Theapparatus according to claim 15, wherein the processor is arranged toallocate another port from among the plurality of aggregated ports,different from the selected port, to serve as a backup port, and toreplace the selected port with the backup port as part of the path,responsively to a service interruption of the selected port.